Human platelets contain a low molecular weight polypeptide hormone that selectively stimulates the growth of connective tissue cells. Our laboratories have recently purified this platelet derived growth factor (PDGF) to homogeneity. We have shown that PDGF is stored within the alpha-granules of intact platelets and is secreted into serum when blood clots. This research proposal has three objectives. The first objective is to study the molecular biology of PDGF biosynthesis and compartmentation into alpha-granules. Specific high titer antibodies to human PDGF will be used as probes to determine whether megakaryocyte cells in the bone marrow synthesize PDGF. Antibodies will also be used to monitor the compartmentation of PDGF into alpha-granules. The second objective is to apply the technologies of genetics and molecular biology to an analysis of PDGF function. A unique selection scheme will be employed to obtain temperature sensitive mutants of tissue culture cell lines which cannot respond to PDGF at restrictive temperatures. These temperature sensitive PDGF mutants will be used to examine the molecular events by which PDGF induces a round of replicative DNA synthesis in fibroblast cells. Pure PDGF will be radioiodinated and receptor binding studies will be performed. Early cellular changes following binding of the PDGF molecule will be examined at the biochemical level. The third objective is to study the structure of the PDGF molecule as it relates to function. Specific amino acid residues within the PDGF molecule will be chemically modified. The effect of chemical modification on PDGF binding and mitogenic activity will be monitored. PDGF will be purified from lower animals including the cow; peptide fingerprint maps of bovine PDGF will be compared to fingerprint maps of bovine fibroblast growth factor and of human PDGF in an attempt to identify highly conserved regions of the PDGF molecule which may have special functional significance.